1. Field of the Invention
This invention relates to a pressure sensor for converting a fluid pressure into an electrical signal, and more particularly, to a pressure sensor of the type including a moveable member which is subjected to a fluid pressure thereby causing a displacement of the moveable member, such displacement being converted into an electrical signal.
2. Description of the Prior Art
Many kinds of pressure sensor have been suggested. For example, U.S. Pat. No. 4,453,412 discloses a diaphragm type pressure sensor which has an amorphous metal member fixed to the diaphragm. The amorphous metal member is stressed by the pressure displacement of the diaphragm and the sensor detects the change in the magnetic characteristics of the amorphous metal member. Therefore, in this type of pressure sensor, which has a detecting structure fixed to the diaphragm, the diaphragm is subjected to fatigue since the normal displacement of the diaphragm is prevented by the amorphous metal member secured thereto. Thus, this type of pressure sensor has a life span which isrelatively short.
U.S. Pat. Nos. 4,488,436 and 4,500,864 each disclose a diaphragm type pressure sensor with a strain gauge affixed to the diaphragm. This type pressure sensor has terminals provided directly on the diaphragm to connect conductive wires to the strain gauge for obtaining a readout. Therefore, in this type of pressure sensor, which has the readout wires fixed to the diaphragm, fatigue will occur in the diaphragm similar to the fatigue experienced by the amorphous metal type pressure sensor. Furthermore, the terminals might become separated from the diaphragm after repeated displacement of the diaphragm since the stress is concentrated at the terminals.
Thus the conventional type pressure sensors have a structural problem whereby the characteristics of the pressure detection are changed by the repeated displacement of the diaphragm. Further, the conventional type pressure sensor has a less sensitive characteristic for a small pressure change since the fixed member on the diaphragm, such as an amorphous metal member or the readout wires, prevents a small displacement of the diaphragm for a small pressure change.